The present invention relates to a tire condition monitoring apparatus that wirelessly transmits conditions of a tire including the air pressure of the tire to a receiver.
Wireless tire condition monitoring apparatuses that allow a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been proposed. A typical monitoring system includes transmitters and a receiver. Each transmitter is located in the wheel of one of the tires and the receiver is located in the body frame of the vehicle. Each transmitter detects the conditions, such as air pressure and the temperature of the associated tire, and wirelessly transmits the detected information to a receiver. The receiver receives data from the transmitters and displays the conditions of the tires, for example, on a display located in front of the driver""s seat.
As shown in FIG. 6, a prior art transmitter 100 includes a pressure sensor 101, a temperature sensor 102, a voltage sensor 103, a transmission controller 104, a transmission circuit 105, and an antenna 106. These devices are driven by a battery 107. The pressure sensor 101 measures the internal air pressure of a tire. The temperature sensor 102 measures the internal temperature of the tire. The voltage sensor 103 measures the voltage of the battery 107. The transmission controller 104 wirelessly transmits the air pressure data, the temperature data, and the voltage data to a receiver (not shown) through a transmission circuit 105 and the antenna 106. In this manner, the transmitter 100 monitors the voltage and transmits the voltage data to the receiver. The receiver displays the voltage, thereby informing a passenger about the voltage of the battery 107.
When the life of the battery 107 expires, the transmitter 100 cannot operate. Therefore, it is necessary that a passenger in the passenger compartment be able to confirm the life of the battery 107 in the transmitter 100. The transmitter 100 thus transmits the voltage data together with data representing the tire conditions. When the voltage represented by the voltage data is equal to or less than a predetermined determination value, the receiver determines that the life of the battery has expires and shows the determination result, for example, on a display device (not shown).
If the voltage of the transmitter 100 is lowered below a lowest operating voltage of the transmitter 100, the operation of the transmitter 100 will be unstable and the contents of transmitted data will be unreliable. Also, every transmission of transmission data lowers the voltage of the battery 107 and consumes the battery while repeating unstable operations. This lowers the reliability of data transmitted by the transmitter 100.
The voltage of the battery 107 varies significantly depending on the environment in which the battery 107 is used. In a temperature range about 20xc2x0 C., the voltage of the battery 107 is maintained equal to or more than the operational voltage of the transmitter 100 (for example, equal to or more than 2V). In an extremely low temperature range of, for example, xe2x88x9240xc2x0 C., chemical reactions in the battery 107 are suppressed. Thus, when a great current is needed for transmission, the lowest operation voltage of the transmitter cannot be maintained, and the transmission can be stopped. In this case, if the data transmission is performed, the voltage of the battery 107 is further lowered and consumes the battery 107, which unnecessarily consumes the electricity. If the temperature about the battery 107 is increased to a temperature level that allows the transmitter 100 to perform transmission, a significant amount of electricity has already been unnecessarily consumed. The life of the battery 107 is therefore shortened.
Accordingly, it is an objective of the present invention to provide a tire condition monitoring apparatus that reliably performs transmission by maintaining a voltage that permits a transmitter to operate even if the voltage of a battery is lowered.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a tire condition monitoring apparatus for monitoring a condition of a vehicle tire is provided. The apparatus includes a transmitter and a receiver. The transmitter is located in the tire and activated by a battery. The transmitter includes a tire condition sensor, a transmission circuit, a voltage sensor, and an electricity control circuit. The tire condition sensor detects the condition of the tire. The transmission circuit wirelessly transmits data representing the tire condition. The voltage sensor detects a voltage of the battery. During a period from when the tire condition sensor detects the condition of the tire to when the transmission circuit starts transmitting the data, the electricity control circuit performs a transmission preparation process to gradually increase electricity supplied to the transmission circuit from the battery, thereby gradually increasing a radio wave output of the transmission circuit. If the value of the voltage detected by the voltage sensor is lowered to a lowest operation voltage of the transmitter during the transmission preparation process, the electricity control circuit limits the supply of electricity to the transmission circuit from the battery. The receiver is located in a body of the vehicle and receives data from the transmitter.
In another aspect of the present invention, a transmitter that is located in a tire of a vehicle and activated by a battery is provided. The transmitter includes a tire condition sensor, a transmission circuit, a voltage sensor, and an electricity control circuit. The tire condition sensor detects the condition of the tire. The transmission circuit wirelessly transmits data representing the tire condition. The voltage sensor detects a voltage of the battery. During a period from when the tire condition sensor detects the condition of the tire to when the transmission circuit starts transmitting the data, the electricity control circuit performs a transmission preparation process to gradually increase electricity supplied to the transmission circuit from the battery, thereby gradually increasing a radio wave output of the transmission circuit. If the value of the voltage detected by the voltage sensor is lowered to a lowest operation voltage of the transmitter during the transmission preparation process, the electricity control circuit limits the supply of electricity to the transmission circuit from the battery.
The present invention also provides another transmitter, which is located in a tire of a vehicle and activated by a battery. The transmitter includes a tire condition sensor, a transmission circuit, a voltage sensor, and an electricity control circuit. The tire condition sensor detects the condition of the tire. The transmission circuit wirelessly transmits data representing the tire condition. The voltage sensor detects a voltage of the battery. After the tire condition sensor detects the condition of the tire, the electricity control circuit gradually increases electricity supplied to the transmission circuit from the battery, thereby gradually increasing a radio wave output of the transmission circuit. If the value of the voltage detected by the voltage sensor reaches a lowest operation voltage before the value of the radio wave output reaches a predetermined value, the electricity control circuit limits the supply of electricity to the transmission circuit from the battery, such that the transmission circuit performs transmission at a radio wave output that is less than the predetermined value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.